Did you see the sky over Bucks County on Sunday night? Mammatus clouds put on a show

It was not a bird, a plane, popcorn, cotton balls or giant cow udders in the skies above Bucks County on Sunday evening.

So what was it?  A unique weather phenomenon.

Called mammatus clouds, these formations are condensed pockets of sinking cold air that form at the base of a cloud as it hits a warmer layer of air creating what, to some, appear to be cow udders in the sky.

What made their appearance Sunday unusual was how widespread it was, appearing as far south as northern Delaware and across New Jersey and the Delaware Valley region, said Patrick O’Hara, a meteorologist with the National Weather Service in Mount Holly, New Jersey.

Amateur photographers didn’t hesitate to flood social media with pictures of ominous and majestic looking skies Sunday night.

“Did anyone look at the sky tonight?  What an amazing cloud,” wrote a poster on the Doylestown Facebook page.

Another person posted:“Suddenly Lake Galena went wild. What a blessing tonight’s sky was."

“Weird stuff in the skies lately,” wrote someone on the Bensalem Proud Facebook page.

“I live five minutes away from the Neshaminy Mall for all my married life and I’d never seen anything like that. That is just bizarre. Beautiful but bizarre for sure," wrote another person.

Here is what we found about about mammatus cloud formations

What types of clouds are mammatus typically associated with

These cloud pouches are most often seen with cumulonimbus clouds, which produce strong storms. These clouds typically form during warm months by descending air in the cloud, according to the UCAR Center for Science Education.

What does it mean when you see mammatus clouds

Potential trouble is coming, or it has passed. Mammatus clouds generally form in the most unstable cumulonimbus clouds (the cloud formations that can produce extreme weather). When that happens they are often a sign of a particularly strong storm.

How do mammatus clouds form?

With big thunderstorms there is a large mass of water vapor that rises to the top of the atmosphere then spreads out as it sinks down, O’Hara said.  Normally, these type of clouds form over a smaller area.

Are mammatus clouds dangerous?

Yes, if you are a pilot. Because they are a type of cumulonimbus clouds that can indicate high levels of turbulence, according to the American Meteorological Society. But for those of us on the ground, they are generally harmless, but because they form in unstable air they can signal the chance of other dangerous weather nearby like lightning or hail..

Are mammatus clouds rare?

They are not uncommon, but they are most picturesque at sunset,  O’Hara said.

Reporter Jo Ciavaglia can be contacted at jciavaglia@gannett.com

This article originally appeared on Bucks County Courier Times: Did you see the sky over Bucks County on Sunday night? Mammatus clouds put on a show